This invention relates to a die-bonding method and an apparatus therefor for adhesively joining or connecting a semiconductor chip onto a portion subject to bonding such as a bed portion of a lead frame by using resin.
The implementation of typical die-bonding is shown in cross section in FIG. 1. As shown, a semiconductor chip 43 is adhesively joined or connected onto a bed portion 41 of the lead frame by a resin 42 such as thermosetting resin, thus to carry out die-bonding. In such a die-bonding, because a quantity of the resin 42 directly affects the bonding or adhesive area and the bonding strength, supply of constant quantity of the resin is important. For this reason, the screen printing method, the stamping method, the dispensing method, the air pressure constant quantity discharge method, and other methods is selected dependent upon the kind of semiconductor chip, the characteristic of the resin used, etc. Among them, the air pressure constant quantity discharge method is the method to discharge resin by air pressure. Since this method is excellent in view of the workability and effective use of resin, as compared to other methods, it has been widely used in the art.
FIG. 2 is a block diagram showing a conventional die-bonding apparatus based on the air pressure constant quantity discharge method. A needle 46 is attached at the lower portion of a resin vessel 45 filled with a thermosetting resin 44. The needle 46 faces above a bed portion 41 of a lead frame supported by a base table 47. When high pressure air is delivered into the resin vessel 45, the resin 44 within the vessel 45 drops off by a constant quantity thereof from the needle 46 onto the bed portion 41. The supply of the high pressure air is provided by a pressure unit 50 connected to the resin vessel 45 via a flow path 48. The pressure unit 50 is composed of a discharge time control unit 51 and a discharge pressure control unit 52. The discharge time control unit 51 serves to adjust the supply time of high pressure air. Actually, this unit 51 controls the drive time of an electromagnetic valve etc. for supply of high pressure air. On the other hand, the discharge pressure control unit 52 serves to adjust supply pressure of the high pressure air, which is connected to a high pressure air supply source 54. The pressure unit 50 thus applies high pressure air to the resin vessel 45 as an air pulse of predetermined discharge time and discharge pressure at a discharge timing from a mount control unit 53, thus, to thrust the resin 44 within the resin vessel 45 from the needle 46.
However, such a conventional die-bonding apparatus has the problem that the discharged quantity of the resin varies with time. This results from changes or variations in the quantity of the resin remaining within the resin vessel, 45 or changes or variations in response to the electromagnetic valve of the discharge time control unit 51. The inventor of this patent application has found that the cause of changes in the resin discharge quantity is that, the resin vessel 45 empties, varies by the discharge of the rising pressure applied to the resin vessel 45 changes. FIG. 3 is a characteristic curve showing measured changes in the discharge quantity when constant viscosity silicon resin is filled within the resin vessel 45 having an internal capacity of 5 cc, allowing resin to be intermittently discharged at a constant pressure. The resin height H (mm) and the resin discharge quantity W (g) correlate to each other when the discharge start time (START) is assumed as "0" and the discharge quantity at the time of end (END) is reduced by 15 to 25%. Namely, since the discharge quantity of the resin correlates with the pressure rising characteristic, the resin discharge quantity varies with lapse of time. This is the reason that a constant quantity or supply is impossible. Such an unfavorable phenomenon has become conspicuous more and more as a wide variety of resins in which viscosity, volatility, or the like, are different, have appeared, multiple point discharge nozzles have been implemented, and resin vessels have become large. This is a problem in respect of quantity resulting from the fact that the semiconductor chips are diversified and have become large-sized.